1. Field of the Invention
This invention relates to a multiple valve engine for a watercraft, and more particularly to an engine for a watercraft that has intake and exhaust valves which are different in number.
2. Description of Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and caries one or more riders. A relatively small hull of the personal watercraft commonly defines a rider's area above an engine compartment. An internal combustion engine powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on an underside of the hull. The jet propulsion unit, which includes an impeller, is placed within the tunnel. The impeller has an impeller shaft driven by the engine. The impeller shaft usually extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.
Because the riders straddle a longitudinally extending seat, which is placed in the rider's area above the engine, the engine is required to be as short as possible in height. Some prior engines therefore have been slanted toward one side of the hull to reduce the height of the engine.
Personal watercrafts with a four-cycle engine are now being designed to reduce exhaust emissions. The four-cycle engine, however, normally has multiple valves and a valve drive mechanism arranged to actuate the valves. The valves and valve drive mechanism are generally made of metal material that is heavier than other materials. If the engine is slanted as noted above, the hull side to which the engine is slanted bears more weight than the other side. This imbalance in weight affects the handling characteristics of the watercraft.
A need therefore exists for an improved multiple valve engine that can aid in balancing the weight of engine with the hull.